1. Field of the Invention
The present invention relates to a writing instrument, and more particularly to a writing instrument in which a stick-shaped object can be extended outwardly of the writing instrument by rotating a tubular body relative to an outer sleeve.
2. Description of the Related Art
A conventional writing instrument is disclosed in, for example, Japanese Utility Model Publication No. 3-397, which includes a cap having a guide sleeve rotatably assembled therein. The guide sleeve has axially extending slits formed therein and an eraser holder assembled thereto with outward projections of the holder fitting into the slits. Therefore, the eraser is movable in the axial direction of the guide sleeve.
A spiral-grooved sleeve is assembled around the outer circumference of the guide sleeve, and includes two half assemblies (e.g., two portions). The spiral-grooved sleeve is assembled integrally with the cap such that the spiral-grooved sleeve is not rotatable relative to the cap. The spiral-grooved sleeve is formed with a spiral groove which receives a tip of the outward projections of the eraser holder. The rearward end portion of a joint is fittingly mounted into the forward end portion of the guide sleeve, such that the joint and the guide sleeve are not rotatable relative to each other. The forward end portion of the joint is fitted into the rearward end of an outer sleeve which accommodates a writing member therein. The joint and the outer sleeve are assembled so that they are not rotatable relative to each other.
A rib-to-groove fitting engagement connects the guide sleeve to the joint such that they are not rotatable relative to each other. Likewise, a rib-to-groove fitting engagement connects the joint to the outer sleeve such that they are not rotatable relative to each other.
However, to fit the rib into the groove, the joint must be angularly accurately positioned about an axis thereof with respect to the guide sleeve and the outer sleeve. Fitting the guide sleeve into the joint, or fitting the joint into the outer sleeve requires a time-consuming assembly operation.
Another problem is that it is difficult to manufacture the rib and groove such that they are precisely configured to each other and such that the assembly does not rattle after the rib and groove have been assembled. Moreover, if the rib and groove are configured to each other with very small gaps therebetween, they are difficult to readily assemble. Consequently, a certain amount of rattling between the guide sleeve and the outer sleeve results.